Full Idea
The most dramatic phenomena undermining the absolute reliability of introspection are those of blindsight and "anosognosia" (unawareness of one's own brain damage).
Gist of Idea
Brain damage makes the unreliability of introspection obvious
Source
Georges Rey (Contemporary Philosophy of Mind [1997], 3.2.2)
Book Reference
Rey,Georges: 'Contemporary Philosophy of Mind' [Blackwell 1997], p.85
A Reaction
It might depend on what you expected introspection to reveal. If you only expected it to tell you about your consciousness, it would be unreasonable to expect knowledge of blindsight information by introspection.